Housing for electrical apparatus



E. slMoN ETAL 2,642,920

3 Sheets-Sheet 1 INVENTORS ELI SmoN FRANx W. THoMAs EDWARD H. BURKART Alenf HOUSING FOR ELECTRICAL APPARATUS ubi il June 23, 1953 Filed Oct. 4, 1950 y; l. E

'Jane 23, 1953 E. SIMON ET AL 2,642,920

HOUSING FOR ELECTRICAL APPARATUS Filed Oct. 4. 1950 3 Sheets-Shea?I 2 S E 25 a F255 g e 2e 7 ,26N l--u-LAMINATING REssN 2 7 ooPo|.YMER BETWEEN LAMINARNG RESIN 25 AND lsocYANATE-coNTAlNxNG MoLEcuLEs REAcTnoN PRODUCT oF ALKYD REslN-onsocYNANATE L INVENTORS ELI SIMON BY FRANK W. THOMAS EnwARo H. BURKART x y` Agent June 23, 1953 E. slMoN ET AL 2,642,920

HOUSING FOR ELECTRICAL APPARATUS Filed Oct. 4. 1950 3 Sheets-Sheet 3 E: IGM

INVENTORS Eu Sm'on BY lFRANK W. Tnoms EDWARD H. BURKART 1 x Agent Patented June 23, 1953 UNITED 4sTnsrT-:s PATENT oFFicE l2,642,920 l HOUSIG'FOR LECTRICLYAPPARATUS .EliSimonrLos-Angeles, Frank-.W. Thomas, -Bur- 1-2l31aims. 1 This invention frelates -zto enclosures, rhousings, panels, etc. -for :electrical apparatus. E`I..he .pres` ent lapplication .is a-r continuationein-.part of Tour copending application, Serial .'No.. 76,952 filed Februaryr11f1f949. Y

The products for devices of lthe invention have many applications, wbeing useful in protecting, housing and .supporting .numerous :classes vof objects and instrumentalities particularly where there isa .need for dielectric :properties coupled with vhighstrength land low-'weightV :characteristics. lWhile :we do not -intend :to vimply any restrictions .on 'the applications -of =.the ,products or articles, the invention :is .particula'rly Well suited :for incorporation mor embodiment in radomes .for housings for .radar equipment, the housings .constructed .in accordance with the invention possessing 4`.excellent dielectric, strength, and vibration resisting characteristics, and being highly l'transparent for 'conductive of "the micro- Awaves .of radar transmission. In certain of `the prior methods -of'con'st'ructing lsuch devices vafcore werejoinedfat'the interfacesby excessively thick and nonuniform layers -of adhesive materials.

VIt vis, accordingly, an object'i of the :present in;- -vention 'to Iprovide :laminated l objects l.and devices 4incorporating one -orwmor'e Iskins an'd a 110W,- kdensiirv core rand having vsuperior strength char- -aoteristics and micro-wave transmission f-charace teristics superior to those of `thehoneycomb vvtype housings, etc. l

Another-object1of ,the 'invention is Lto provide an varticle or device ofthe ,general character ire- .v'ferred Ato having .a :core Alayer or :lamination integrally and intimatelyjoined or bonded .directly .withV the `skin 'laminations The lcore1is vreacted and# cast directly between the skin laminations fat `the timethe housing or device fis constructed iso :to 'adhere directly to Vthe :skin `ilamiriatio'ris` 'to ia stronger product iaving rnore `tira-- rform micro-'wave transmission characteristics etc.'

J2 articles of the general class referred toin which the materials 'fof fthe -c'ellular core .and Ythe .lamif natingresin=fof the :skins are chemically united to cbtainthe greatest'possible strength. In the structures of the invention vwhere -the` cellular corematerial is reacted between the laminated skins impregnated with funpolymerized resin, ythe re'a'ctant zmixture of Vthe core lmaterial and the laminating :resin of the skins intermingle Yand unite chemically in zones which may consist primarily vkof copolymers Lbetween the laminating resin and the :resin-polyisocyanate mixture of the core with molecules vo'f both the resin -and the lmixture r*interspersed therein. These interfacial yzones .of intermediate composition are coextensive with the marginal Aareas of the core and with at least certain vof the flaminations of the fskin, thereby fstre'ngtheningthe structure by ineludingin'thelskin-laminae-some of the resin'- -polyisocyanate foam with `its inherent .high strength characteristics. Thus -the products -of the vinvention `are Vdifferentiated :from the `laminated vstructuresv of the fprior -art `where the core material and the skin laminations were joinedat l-by 1n'iechanica'l interlocking of the core `material vand. `-the vmaterialor fabric of the skins.

In accordance Vwith lone embodiment lof the invention .the cloth-orfabiicof the skins is provided with 2a v`laminating :resin in manner -to cover -or. coat the individual `threads or 'fibres of the yfabric `.and

:yet jllea've pores 'or openings between .the same yand the lcore --material is reacted between the kskins -to ie'nterand fill vthese -pores to-obtain the mechanical `lock and =to unite chemically with the laminating resin to 4obtain- -th'e chemical union, or to *adhere to the individual resin coated threadsof the -c1oth, The laminating resin aplplied-to `the 4skin fabric maybe `wet at the time ithe -cofe :material is L-poure'd `to v obtain a diffusion region 1inwhich y:there 'is eopolymerizaticn of the core .and '-skinresins to 'eiect .the-.chemical `union or the -f-fresi'ns fof the fski-nsfand .oore, or the skin .Another .eb'jcc't lef :the invention to aprende .#55 'resinimay te 'setfor hersenen anacured so niet there is adhesion of the core material with the resin impregnated fabric as well as the mechanical locking engagement of the core material in the pores of the fabric. If desired, the resin applied to the fabric may be allowed to set and cure and the skin may be preformed and then immediately prior to the pouring of the core material a second resin may be applied to the porous resin-coated skin to obtain a copolymerized diffusion zone and the penetration of the core material into the pores of the skin. AIn Veach of these modes of procedure the strength of the bond of the skin with the core approaches the strength of the core, the potential physical characteristics of the foamed core material being effectively utilized.

Other objectives and features of the invention will become apparent from the following detailed description of typical preferred embodiments in which reference will be made to the accompanying drawings where: 1

Figure l is a vertical sectional viewl illustrating skin laminations on the surfaces of male and female moldparts and showing the unreacted core material in the mold;

Figure 2 is a view similar to Figure'l illustrating the core material in the foamed or cellular condition showing the manner in which the reactant core material holds the skin against the surfaces of the mold;

Figure 3 is an enlarged fragmentaryperspective View of the structure or product made in accordance with the invention;

Figure 4 is an enlarged fragmentary sectional View illustrating the several laminations` of the skins and the core of the product;

Figure 5 is a diagrammatic view on a greatly -enlarged scale illustrating the skin and an interfacial region of the product showing the interspersion of the cellular core material and the laminating resin of the skin;

Figure 6 is a greatly enlarged fragmentary vie of one of the untreated skin laminations or fabric layers;

Figure 7 is a view similar to Figure 6 showing the laminating resin applied to the fabric;

Figure 8 is a fragmentary sectional View with the fabric appearing in elevation and illustrating the material of the core occupying the pores in the resin coated or impregnated fabric of the skin; and

Figure 9 is a fragmentary sectional View taken in a plane normal to the plane of sectioning of Figure 8 illustrating the mechanical lock or engagement of the core material with the resin impregnated skin fabric.

The products or devices of the invention may vary greatly in their intended use or application. For example, the devices may be panels, sheets, or covers, or may be housings, casings or containers of simple or complex shape for electrical devices and other mechanisms of different kinds. As above pointed out, the devices or structures of the invention transmit radar energy, etc. with a minimum of loss and we will herein describe the invention as embodied in shells, housings, or domes, for radar transmitting and/or receiving equipment, it being understood that this is only one typical application of the invention.

It is believed that the characteristics of thel products of the invention will .be best understood by describing the materials employed and the methods of producing the' products. InV one method or manner of making the articles the outer laminating material or skin material I4 is 4 provided on the surfaces of a mold I0-I 2, a reactant alkyd resin-polyisocyanate mixture I5 is introduced into the skin-lined mold cavity and allowed to react to form a cellular core I6 between and bonded with the skin laminations I4 and the resultant laminated structure may then be post-cured at slightly elevated temperatures.

The mold incluudes a female part I@ having a central cavity II and a male part I2 conforming generally in shape with the cavity. The upper .end of the cavity II remains open to the atmosphere at all times while it lower end is closed.

lThe mold cavity II of course may be of any requiredy or Vdesired shape and in the particular case illustrated is spherically concave at its lower end. The male mold part I2 is shaped so that its external surface is substantially parallel with and equally spaced from the wall of the cavity I l when the mold parts are in their final positions. The part I2 is adapted to extend upwardly beyond the upper surface of the part I0 and' its projecting portion has spaced radially projecting lugs I3 which are adapted to rest on the part I0 to support the male part I2 and may, if desired, be constructed to obtain the desiredspacing between the walls of the cavity II and the surface of the part I2. i

The'abovementioned outer or skin materials I4 are arranged to coverI or line the surfaces of the mold. These materials I4 will, of course, vary in character, depending to a considerable extent upon the intended use of the product being manufactured. Where the product or housing is designed for the transmission of radar or micro- Wave energy, the skin materials I4 may be fibreglass fabric, superimposed layers of non-impregnated nbre-glass cloth, felt, fibre-glass matting, or other materials that are substantially transparent to radar energy. While in most cases it is preferred to employ a plurality of superimposed layers of such material I4, on the surfaces of the cavity I I and mold part I2, Figures l and 2 illustrate, for the sake of clarity, only one layer or thickness of the fabric I4 on each mold surface. In Figures 4 and 5, where'the product is illustrated on a much larger scale, there are pluralities of the skin material layers I4 on each side of the housing or product.

The skin materials I4, Whether employed as single layers or as a plurality of superimposed layers, are preferably arranged to completely cover the Walls of the cavity II and the surface of the mold part I2, at least to the height where the housing is to be trimmed off or finished. The skin materials I4 may either be preformed and prelaminated, that is impregnated with a laminating resin and then formed and shaped to fit their respective mold surfaces, the resin being cured so that the skin materials are substantially rigid and self-supporting, or the skin materials I4 vmay be unlaminated and without resin, either 'cured or uncured, in which case appropriate care is taken toarrange and support the soft, unformed skin materials i4 on their respective mold surfaces. Where the skin materials I4 have a plurality of layers, it is preferred to offset the i basic acids unmodiedormodifled with oil and/ or other resins and having an acid'nuinber of from 'to 80, .a `'waterfcontentof .fromfOll ltor-approximately 3.0% `by :weight and having the following .rationange :of :thehydroxylto the carboxylfgroups inthe alkyd rresinzrea'ctants: from 13 hydroxyl 7CH-)f1 carboxyl iiCOOI-I) to 4 hydroxyl (OH) :5 carboxyl (COOH).

It is usually preferredto employ :alkydc'esinslhaving an acid Anumber of betwe'en 1D fand kizy'ia'md wherein the ratio :of fthe 'hydroxyl .groups '.to 'the carboxyl groups is 2 to 1. The'following formulae are suitable for preparingunmodiedialkyd resins from polyhydri'c alcohols `vand polybasic acids, the ratiosl of 'the khydroxyl VAgroups lto Vthe carboxyl groups in the alkyd -resin reactants of these formulae being`2 -tol. Y

FORMULA A Mols Glycerol f4 Adipic-"acid 2.15 Phthalic :anhydride :5

FORMULA .B

. Mls

Glycerol n 12 1, 4 butylene glycol 1 Adipic acid 2 FORMULA C MOIS Trimethylol propane, -4 Adipic acid. 2.5 Phthalic anhydride 0.5

In Formula A'from 3 to -5 'mols vo'l glycerolxfrorn 1.5 to `3fmolsadipic acid'and'from"0.1`to 15 mols of phthalic "anhydride may `loe :used While in Formula C the'practical operative range of proportions is vfrom `3 to '5 -mols Atrimethylol propane, from 1.5 to 3 mols adipic acid and from 0.1 to 1.5

mols of phthalic anhydride. The following For- `rnu'lae D and E are suitable for preparing unmodied alkyd 'resins from 'single polyhydri'c alcohols and `'single polybasic racids productive of resins `suitable for Vuse in the -fcellular plastic mixture.

The ratio of the hydroxyl 'groups .to the carboxyl groups in the alkyd Avresin lreactants of lFormula .D is 2(0H) 1.1(COOH) `and .in .Formula this .ratio is 9(OH) :4(-COOH-).. .The :following IFormula F is anexample .of .an oil modified alkyd .resin suitl VThe,followingflformula G isan example of a natural'resinrnodied alkydresin'suitable for incorporation in the cellular foamed plastic core material, the ratio of the hydroxyl to the carboxyl groups being '1v-to 1.

. FORMULA -G 'Glycerol gram moll Sebacic acid 'd'o 1 1/2 Resin copal grams '100 y Wehavefoundth'at the most satisfactoryresults arero'btained vwhen the `water `content range of the alkyd Aresin component of the diisocyanate alkydresin reactant mixture is from 0.1% Ato 3.0 by weight without regard to the specific manner of incorporating the water in the mixture. In the typical A'examples herein set forth, it will be considered that the water component of the diiso'cyana'te-'alkydresin reactant mixture is incorporated by `dissolving a calculated amount of the Water 'in the selected alkyd 'resin and suitably agit-,ating` the resin-water mixture so that the alkyd resin lcomponent will contain the selected proportion of water.V However, as set forth in thecopending application of Eli Simon and Frank W. Thomas, Serial No. 35,294,1'iled June 25, 1948, the Water may be incorporated in the reactant mixture in combination fwithfa' nonlionic wetting agent or by the use ofone ormore salt hydrates.

The isocyanate employed in thefalkyd resin polyisocyanate `reactant mixture is preferably able for employment in the reactant cellularplas-f tic producing mixture, V.the fratiolof .the .hydroxyl groups to the carboxyl groupsjinthe resin reactant being 3(0H) :Sl/(COOH).

metal-toluene diisocyanate. `described and .claimed in the copending application of .Eli Simon and Frank W. Thomas, Serial No. 50,007, led September '18, 1948, Vmetallic soap powders may be incorporated in the diisocyanate alkyd resin reactant mixture to serveas foaming agent stabilizers and thus obtain superior results. The metallic soapjpowders that are effective for this purpose are metallic soap powders of fatty acids having from 12 to 20 carbonatoms inclu-ding:`

vZincstearate Aluminum stearate .Calcium stearate Magnesium stearate Magnesium hydroxy stearate Barium stearate f f Zinc laurate Calcium oleate Strosritium stearate.

.The proportion oi the metallic soap powder em- Tuary 17, '1949, discloses the incorporation inthe alkydV resin-meta-teluene diisocyanate-water `system o'f high `molecular weight thermoplastic viilm producing 'polymeric resin 'additives which fserve `as "lm stabilizers. V'These additives result in theproduction 'of`foamed plastics having very smalluniform cells and having superior physical strength. Furthermore, the additives permit the use of a high water content in the alkyd resinmetatoluene diisocyanate system, for example a y water content of by weight, thus reducing the density of the cellular plastic material. Further, it has been found to be particularly advantageous to employ the high molecular weight polymeric additives in the cellular plastic material of the cores where the product or articles of this invention are to be used in association with radar equipment.

The high molecular weight polymeric resin additives are soluble in the meta-toluene diisocyanate and may or may not react therewith. Included among these additives that are productive of a more eiective small cell foamed plastic core material are:

1. Ethyl cellulose: This polymeric resin has a molecular weight of approximately 130,000 and it is preferred to employ an ethyl cellulose having from 45.0 to 49.5% ethoxyl content. The best results have been obtained Where the viscosity is between 50 and 100 centipoises a1- though the viscosity may range between '7 and 200 centipoises.

2. Polymeric chlorinated natural rubber: This product has an average chlorine content of 67% and a preferred viscosity of between 125 and 1,000 centipoises.

3. Polymeric acrylate and methacrylate resins and their copolymers (prepared by polymerizing lower esters of acrylic and methacrylic acid):

. Methyl methacrylate Propyl methacrylate Isobutyl methacrylate Butyl methacrylate methacrylate.

a. Containing approximately 87% vinyl chloride and 13% vinyl acetate and having a molecular Weight of approximately 6,000 to approximately 25,000.

b. Containing from 90% to 95% vinyl chloride.

10. Polyvinyl acetate (produced by polymerization of vinyl acetate). The molecular weights of the polyvinyl acetate suitable for incorporation in the cellular plastic formulation range fromv approximately l10,000 to approximately 50,000.

11. Polyvinyl chloride (having an average molecular weight of approximately 5,000).

The Y concentration or proportion of the selected high molecular weight polymeric resin employed may be Varied considerably. For example, from 0.03 gram to 15 grams of the ethyl cellulose or from 5 to 20 grams of the chlorinated natural rubber may be used with each 100 grams of the meta-toluene diisocyanate as incorporated in the reactant cellular foamed producing mixture.

The cellular plastic core material employed in Clo-polymer of methyl acrylate and ethyl the core I6 of the product of the invention may be made flame resistant and self-extinguishing when once ignited by incorporating lflame retardant additives in the alkyd resin-meta-toluene diisocyanate reactant mixture. Such additives are unsaturated alkyl esters of aryl phosphonic acids, namely compounds having the general formula:

Where Ar represents aryl and alkaryl hydrocarbon radicals andvR, and R1 are hydrogen and alkyl hydrocarbon radicals. Compounds of this character are described in United States Letters Patent No. 2,425,765 issued August 19, 1947, and include:

1. Diallyl phenyl phosphonate 2. Bis(methal1yl) benzene phosphonate 3. Diallyl toluene phosphonate.

These additives, in addition to imparting ame resistance and to decreasing flame propagation characteristics of the foamed cellular product, also serve to materially decrease the density of the foamed material. vIn practice, from 1 gram to 20 grams of the flame resistant additive may be employed with each 30 grams of the alkyd resin. Where such re resistant additives are employed, it may be found desirable to predissolve benzoyl peroxide in the additive inthe proportion of approximately 5% by weight of the additive.

The following are typical examples of the alkyd resin-metatoluene diisocyanate reactant formulations for the core forming mixture 15:

Example I f y Grams Alkyd resin of Formula C' having an acid number of 20 and a water content of 0.85% by weight 60 Meta-toluene diisocyanate containing 2 grams of ethyl cellulose, having a centipoise viscosity of '7 and an ethoxyl content of fro-m 46.8 toI 48.5 per grams of the metal-toluene diisocyanate 40 Diallyl phenyl phosphonate 10 Benzoyl peroxide 0.5

Example II Grams Alkyd resin of Formula C having an acid number of 20 and .a water content of 0.85% by weight 60 Meta-toluene diisocyanate containing l gram of ethyl cellulose, having a centipoise viscosity of 200' and an ethoxyl content of from 46.8 to 48.5 per 100 grams of the meta-toluene diisocyanate; 40 Diallyl phenyl phosphonate 10 Benzoyl peroxide 0.5

Example III Grams Alkyd resin of Formula C having an acid number of 20 and a water content of 0.85% 'by weight 60 Meta-toluene diisocyanate containing 0.03

gram ethyl cellulose of 100 centipoise viscosity and from 48.0 to 49.5% ethoxyl content per 100 grams of meta-toluene diisocyanate 40 Diallyl phenyl phosphonate 10l 'Benzoyl peroxide 0.5

garage@ 9 EampZefI-V Y Grams- Al-kydresn of' Formula C having' an acid number of 20" and a Water content' of 0.85%- by fweight Meta-'toluene 'diisocyanate-containing 2-grams of ethyl cellu'loseiof'100` centipoises viscosity and 'an ethoxyl content or .from '48.0 to 49.5%. per 100 grams of meta-,toluene diisocyanate' il)l Diallyl phenyl phosphonate- 1'0 Benzoyl peroxide n Example' V Grams Alkyd resin of Formula Ahaving an acid number of 16 and a wateinecontent: onf.:

0.87% by Weight 30 Meta-toluene diisocyanate Zinc stearate powder 2 'Diallyl phenyl phosphon'ate 5 Benzoyl peroxide 0.25

Ezvample VI 1 Grams Alkyd resin of Formula G having an acid Vnumber of 20 and a; Water content of 0.85% by Weight ..30 Meta-toluene diisocyanate containing' 5' grams' of chlorinated natural rubber of 1,000 centipoisesf viscosity per." 1'00 grams of meta-toluene diisocyanate 20 Diallyl phenyl phosphonate 5 Benzoy1 peroxide 0.2.5

Example VII Grams Alkyd resin of Formula C having anvacid number of 20 and a water content of' 0.85% by weight Meta-'toluene diisocyanate.containing 4 grams of benzyl cellulose per 100' grams I Alkyd resin of FormulaA- having an acid number of 1.44 anda. watercontentof 0.31%

by Weight n 30 Meta-toluene diisocyanate 20 Aluminum stearate powder 1 Example X t' 'Grams Alkyd" resin of Formula A having an acid, Y `Ynumber of 34. and a Water content ofilnlat f l by Weight 30 Meta-toluene diisocyanate. 221/2 Aluminumleang-powder 11/2 7g.

When-.the articlebeingproduced is required to transmit; radar energy it is' not' desirable or practical` to incorporate metallic leang powders in the formulations.

The abovementionedlaminating resins applied to or impregnated in the skin materials I4 may be thermosetting plastic resins orblends or mixtures -of thermosetting` resinst andy thermoplastic resins. The laminating resins of the skin materials! llllare capable of copolymerizing with the foaming alkyd resin-diisocyanate reaction products to result in diffusiorrzones of cured or hardened resins, which zonesare characterized by a gradual grada-.tien in content from substantially pure laminating resin in the outer portions or laminae of the skins I4; to intermediate areas at the interfaces of the core.' I6 and skins l containing laminating resin molecules, alkyd resindiisocyanate reaction. product molecules and molecules of the co-polymer between the laminating resin and the reaction product and thence to the substantially pure alkyd. resin-diisocyanate reaction products of the core i6. The nature of these diiusion zones, as We believe them to be ..3 constituted is illustrated in Figure 5 Which'dia-v grarnmatically represents on a large Scalea small `area of a skin I and adjacent portion of thecore i6 in cross section. In AFigure 5, as indicated by the legends; the material of the core i6, that is 1 the reaction productsof alkydfresindiisoeyanate mixture are" represented by' the circles 2f5, the laminating resin molecules are represented;- by the circles 25-enclosing theV crosses',` while the copolymer between the laminating resin and the isocyanate containing molecules are represented by the circles-'2LT enclosing theldia'gona'l lines. It will. be seen from.. an.inspection of Figure 5 that the interfacial area, where the mass of the core 50.` physical composrtronand physical characteristics of abrupt change from one material to the other.-

compounds including:

adjacent lamination M.

I6 joins the innermost skin layer l 4, has substantially equal numbers 0f,- thel three above named molecules 25, 26 and 21, while there is littleor no penetration of the substantially pure core niaterial molecules'A-25into the skin I4 there are a considerable number of the co-polymer molecules 21 between the innermost skin layer lil and the The number of these molecules of the co-polymer gradually lessen in the succeedinglaminations Iflunti'lv there' may be none in the outermost skin lamination. The diffusion areas or'zones of' graduated or merging assure great strength in the laminated or sandwich-type product resulting in a product much superior to the'typical laminated structures where there are distinct planes or limited sectional areas The laminating resins capable 0f copolymerizing with the reaction products of the alkyd resin and diisocyanate of the core l'may be selected from substantially difEerentcIasSeSof resins or (a) Unsaturated polyesters containing more than oneigvinyl group per molecule so kas to be capableof cross' linking and forming insoluble thermosetting type resins. Included ingthis classification.; are the reaction. products of maleic anhydride with a glycol such as di-ethylene glycol which, after the initial reactionV are further heated, and condensedto yield the linear polyester:

() Unsaturated alkyl esters of aryl phosphonic acids such as disclosed in United States Letters Patent Number 2,425,765 issued August 19, 1947. Included in this group are the following:

(1) Diallyl phenyl phosphonate CH2=CH-CHZO-iL-OCHQ-CH=CH2 (2) Bis(methally1) benzene phosphonate (3) Diallyl toluene phosphonate (c) Unsaturated alkyl esters of alkenyl phosphonic acids of the general class disclosed in United States Letters Patent No. 2,425,766 issued August 19, 1947:

(l) Diallyl isobutene phosphonate (2) Diallyl styrene phosphonate Hrs@ ` (3 Bis(metha1lyl) styrene phosphonate (d) Diallyl phthalate Y ll H (e) Allyl, methallyl or crotyl glycol carbonates, such as bis(allyl)diethylene glycol carbonate:

(f) Giycoi naarmate H Il ERIE-O- HC-O- If desired, the laminating resin may comprise a blend or mixture of a selected unsaturated polyester, such as above named, and a monomeric compound which serves as a copolymerizing additive. For example, the unsaturated polyestervbetween diethylene glycol and maleic anhydride with the polymerization carried to and acid number of from l0 to 40 may be mixed with any of the following thermoplastic monomeric yvinyl compounds, each having one vinyl group per molecule to constitute the laminating resin.

(a) styrene (vinyl benzene) (c) Acrylonitrile (vinyl cyanide) (d) Vinyl acetate (e) Vinyldene chloride (g) Diphenyl ethylene c=oH (h) Methyl vinyl ketone there may be from l() to 100 parts by weight of the monomeric compound for each 100 parts by Weight of the unsaturated polyester resin.

The present invention, being directed to the laminated products, is not directly concerned with the theoryv of the chemical action or mechanismY attending the copolymerizing of the isocyanate containing molecules of the foaming core material I5 with the laminating resin. However,

gemeen elongated: iin thea vertical direction. due te# the;

friction orv resistance to vertical motion offered' bystherpre-cured skin. The resultant elongatedv cellslof` the core I6.v are somewhat weaker than the uniform andk substantially spherical cells of the internal areas ofthe core lyleavingaweak interfacialzone. However, when the skin laminating resin is uncuredat'the time the core material' I5 is reacted: `in ther mold; this elonga- (addition reaction withfterminal OH) group'- resulting in (reaction ,with terminal 81C O'QH) group I esult- H Il; ;V ing inamde Structure and 'berating carbondioxide) R-N- C-CH (2') vBy the addition copolymerization activated isocyanate groups of the corev material I5 with the activated vinyl groups,` of

the laminating" resin. Thus:

diallyl phenyl phosphonate Peroxide-type catalyst (benzoyl peroxide) heat It is to be understood that1when1 the.laminate ing resin on, or incorporated. in, the-'skin ma. terial I4 is unpolymerized andinaliquidor;semif liquid state when the reactant core producing material or mixture I5 is introduced into the mold cavity and allowed to react. The reaction of the material I5 is accompanied by the development of gas pressure which urgesthe skin materials I4 outwardly into conforming engagement wththe walls. of themold and which brings the reactant foaming. isocyanate containing. mixture I5 Ainto direct and intimate contact with thef laminating resin so as to admix therewith. This admixing of the foaming isocyanate containing mixture I5-with the laminating-resin is important in that it not only brings about the above described copolymerization of the two materials but also because it reduces the friction between the rising foaming mixture I5 and the skins I4. When the foaming core material I5 rises v.along the:Y surfaceof la'i dry-- pre-cured lamina-terr' .skin-` the marginalf cellsofe'the vcore-456 -iareifoundtbe tatched to an isocyanate group l4 E C-N-R II 0, formulation oi'aurethane) tion erthefoutermost..ceneoffthefcere le resumi- Off theY natedgor at leastreduced and because.- theabove` described:interfacialy zone contains `the copolymer of*A the vcorev material and:- the laminating resin, the. interfacial zone is materiallyy strengthened' instead: of:v being weakened.

Following the introduction of the reactant plastic material I5:` into the lined female mold:

. I0; the-.male mold part I2., carrying'itsskin. ma-

terial: I4; is entered into the cavity II and prop erlyr positioned with: respectv to themold part I0'. Figure. 1? showsxthe mold. part., I2. being' entered into the: cavity II'. It, will bel observ'edthatv4 the.

introduction,V of the part I2 into. the cavity III partially` displaces the reactant alkyd resinpolyisocyanate: I 5 .upwardly in the: moldfandf that the upper. end ofgtl'iezmold` cavityA I I remains open.

to the atmosphere.` The alkyd resin-poly.- isocyanate mixture reacts at atmosphericA prese sure to; produce a. multitude ofv small uniform sphericallyv shapedfgas filled. cellsl throughout the entirecorel and the. foaming plasticv mass rises in the mold space to spill over the top of the mold` lula-r plastic I6- adheres to and bonds with thev inner surfaces ofthe laminated material` II.v The resin. employed in the: prelaminated 'skin material IA-ispreferably compatible withthe alkyd' resin,-

polyisocyanate mixtureV but in any event the lattmfysecurelyK bonds withand adheresto practical- Y v ly' all` skinmaterials. andthe laminating resins` incorporated therein. When the skin materials Mareprelaminated and'.` preformed and' contain polymerized-` cured: resins .or plastics, the material of the cellular plastic core I6: does not penetrate the skin materialsl dfto any. appreciable extent andlwill notengage'or adhere; to the wallsv ofl the-cavity. I I `orfthe surfaceY of the mold'part I2. The; product' or housing is then preferably postecured. in the mold'atfy a temperature of from e 1259111. to- 225 F. for up` to -24 hours tocontinue theproduct is removed from the mold.

When theskinmaterials I4 are noty prelaminated.` andgnot preformed but are inthepnature.

7B? of one or-more layers ofdry, porous or soft oil, or the equivalent, as a parting material. such cases, if desired, a preformed flexible stripfabric, felt, or the like, the reactant alkyd resinpolyisocyanate mixture I penetrates the skin materials I4 as it reacts and rises in the mold assembly and, therefore, will reach the wall of the cavity II and the surface of the mold part I2. Accordingly, it is desirable in this case to coat or cover the surfaces of the mold parts with a parting material prior to arranging or positioning the skin materials I4 in the mold so that `the alkyd resin-polyisocyanate mixture will not adhere to the mold wall. Graphite, deposited from oil-dag, water-dag, or alcohol-dag, a" silicone I6 resin-diisocyanate reactant mixture I5 is allowed or caused to react in the mold space defined by the Wet skin materials so that the foaming alkyd resin-diisocyanate reaction product copolymerizes with the laminating resin to produce or provide diffusion zones of cured or hardened resins in the product. 'I'hese diffusion zones which are coextensive with the marginal portions of the core I6 as well as with some or all of the laminated or single-ply skins I4 are areas Whose compositions graduate or change gradually from substantially pure laminating resin oil, or mineral oil, or the like, may be used as the parting material. When the article being produced is tov be used with radar equipment it is preferred to employ a silicone oil or mineral In pable bag of plasticized polyvinyl alcohol may be used to line the mold, and the reactant mixture will not adhere to such a bag. The penetration or partial penetration of the Askin materials I4 by the reactant alkyd resin-polyisocyanate mixture I5 results in a particularly effective lamination or bonding of the several layers of the skins I4 and a strong uniform and continuous Abonding or merger of the skins I4 with the cellular core I6. The material I5 that enters the skins I4 and that occupies the Zones at the inner faces of the skins I4 reacts in the same manner as the material I5 in the main mass or body of the core I5 to produce a cellular high-strength, low-density plastic characterized by the small cells of substantially uniform size and shape. The cellular plastic coats, embeds and bonds with the fibers, strands. layers, and threads of the skin material so that the skins I4 are, in effect, cast or embedded in the self-same material constituting the core I6 resulting in a product or structure of great strength, uniform composition and substantially uniform physical characteristics and of uniform transparency to radar or micro-wave energy. Upon completion of the initial reaction of the core I6 the product or housing may be postcured in the mold assembly at a temperature of from 125 F. to 225 F. for up to 24- hours.

The products or devices produced as above described each comprise a continuous one-piece core I5 of foamed or cellular low-density plastic and internal and external skins I4 of fibreglass fabric, felt, or the like, laminated and impregnated with resin or plastic. The sandwich-type construction is extremely strong and yet has a very low-density owing to the lowdensity cellular plastic core I5. The products may be produced to have good dielectric characteristics and to pass or conduct micro-wave energy with but slight loss. The products may be cut or machined as found necessary and it is usually preferred to trim off the rough or uneven upper or open ends of the products or housings to bring them to the desired size and configuration.

Instead of employing prelaminated and preformed skins I4 or dry, unformed skins I4, in the manufacture of the devices provided by this invention, the skins I4 may be one or more layers, sheets or plies of fibre-glass fabric, fibreglass matting, felt, or the like, or combinations of such materials initially in the dry-soft condition and then wet or saturated or partially saturated with what we will term a laminating resin prior to or at the time they are arranged on the surfaces of the mold Ill-I2. The alkyd to substantially .pure alkyd resin-diisocyanate reaction products of the core. One of these diffusion interfacial zones is illustrated diagrammatically in Figure 5 on a greatly enlarged scale and has been fully described above.

We have found that articles such as housings, radomes, etc. of uniform micro-wave energy transmission characteristics and having excellent resistance to gun blasts, vibration, shock and changes in temperature and atmospheric pressure, are obtained when the skins or skin materials are provided with a laminating resin in such a manner that the skins remain porous. These skins, which are designated in Figures 7, 8 and 9 by the general reference numeral 50, are preferably constructed of one or more plies, layers, or laminations of fibre-glass cloth, or the like, although other fibrous materials may be employed, if desired. In Figures 6 to 9 inclusive, We have illustrated on a greatly enlarged scale, a single layer or ply of fibre-glass cloth 5I and will describe the manner of providing the cloth with the laminating resin 52, it being understood that these drawings are more or less diagrammatic and that in practice each skin may comprise two or more such plies or layers. It will be observed in Figure 7 that the resin 52 coats or covers the individual threads, fibres, or strands of the cloth 5I and yet does not fill or close the through addition polymerization in the presence of a peroxide type catalyst to form a thermosetting type resin. Such non-volatile laminating resins, capable of cross-linking to form thermosetting polymers, which we have found to be practical for the purpose are:

1. Diallyl phthalate H C-O CH2-CH=CH1 2. Diallyl phthalate pre-polymer (a solutionr of low molecular weight polymer in monomer). 3. Diallyl phenyl phosphonate 4. Diallyl phenyl phosphonate pre-polymer (bodied diallyl phenyl phosphonate).

i7 5. Glycol diacrylate cH-o-c|J-CH:CH,

, 6. Bodied glycol diacrylate.

s. Bodies any1 diglycolcarbonate. 9. `Diallyl maleate and bodied diallyl maleate CH-Co o cHioH=oH2 H-C o o CHZCH=CH2 l0. Diallyl fumarate and bodied diallyl fumarate cH2=cHCH2oo o-CH r Ho-o o o CHZGH=CH1 ll. Diethylene glycol 'maleate y Ho [-cHfoHio oH1oH,ocH1-cH=oH--o]on l2. Diethylene glycol maleate-l-diallyl Iphthalate. 13. Diethylene glycol maleate+diallyl phenyl phosphonate.

The volatile solvents forthe above non-volatile laminating resins which .may be used individually or in mixtures are:`

Methyl ethyl ketone Ethyl acetate Trichlorethylene Benzene.

ably about 50% by weight of the resin. The skin or cloth 5I to be treated is then weighed, it being preferred to weigh each ply or sheet separately. The weight of the ply or sheet is then taken into account to determine the amount of the resinsolvent solution that will be required to give the sheet a preferred 20 to 25% by weight loading of the resin although a loading of from 15 to 30% by weight may be used if desired. The cloth plies 5I of a given skin lamination are then saturated with the amount of the resin-solvent solution thus determined. This may be done in any practical manner as by painting, dipping, with rollers or the like. The solvent is then allowed vto evaporate to leave the resin 52 deposited on the libres or threads 5| of the cloth. A mild heat of below 150 F. may be used to hasten the solvent release. The plies thus treated are then laid up in the mold Ill-I2, that is it is arranged on the walls or surfaces of the mold as above described and cured at approximately 200 F., using a vacuum bag as a source of pressure, to produce a preformed cured or rigid porous skin.

The above described manner of treating the sheets or plies 5I results in porous laminations 50 18 that are penetrated by the alkyd' resin-polyiso.- cyanate-reactant core forming mixture, or other ofthe above described reactant core mixtures, when the latter reacts in the mold space or cavity. As illustrated diagrammatically in Figures 8 and 9, the cellular adherent core material I5 lls the pores 53 of the skin 50 moving into the pores under the pressure developed during its foaming reaction vto completely occupy all voids in theskin. The material I5 thus ydirectly contacts and adheres to the laminating resin 52 on the fibers or threads of the cloth and obtains a secure mechanical locking contact or engagement with the resin coated fibers or threads. When the fibrous skins 50 are used it may be desired or necessary to apply a parting compound or material such as above described to the surfacesvof thel mold Ill-I2 before laying theskins in the mold. The

resin impregnated vskins 50 are much easier to handle than the untreated dry skins. We have found that excellent high strength products are obtained when the resin impregnated skins are laid up in the mold 'in the dried or set and preformed condition or when laid up in the mold in the wet state. The cured rigid and preformed porous skins I4 produced, as just described, may be wet or provided with a laminating resin such as above described, and the core forming material I5 caused to react between the spaced skins while the resin'on the skin remains wet. In the latter case there is a copolymerization between the laminating resin on thepreformed skins and the foaming core material I5 to produce a chemical union and a graduated or blended structure such as illustrated in Figure 5. In either case the resultant product or article is highly resistant to the effects of gun blasts and the skins and core are less likely to separate under the inuence of vibration, shock, temperature changes and pressure variations and are very uniform in the transmission of radar energy, etc.

Having described only typical forms of the invention we do not wish to be limited to the specif ic details herein set forth, but Wish to reserve to ourselves any variations or modications that may appear to those skilled in the art and fall within the scope of the following claims.

We claim: y

1. An article of manufacture comprising spaced skin laminations of fibrous materials, laminating plastic impregnated in said materials, and a core layer of cellular plastic material cast between said skin laminations, there being interfacial zones at the planes of joinder of the core layer and skin laminations containing said laminating plastic, said plastic material of the core layer, and a copolymer of the same.

2. An article of manufacture comprising spaced apart skin laminations of brous material, plastic impregnated in the skin laminations of the class adapted to copolymerize with isocyanate-containing molecules, and a core layer of cellular alkyd resin-diisocyanate-ethyl cellulose plastic cast between the skin laminations so as to bond therewith, there being interfacial zones at the areas of joinder of the core layer and skin laminations containing said plastic of the skin laminations, the plastic of the core layer, and a copolymer of the same.

3. An article of manufacture comprising spaced Y 19 tic'castbetWeen-the skinflaminations so` as to bond therewith,` there being interfacial Zones-at the areas of joinder of thecoreu layer and skin laminations containing said plastic of the skin laminations, the plastic of the core layer, and a copolymer of thevsame.

4. In anA articleof manufacture the combination of a porousY fibrous. skin, resin on theskin in the amount-of from 15 to 30%V byl Weightv of the skin Whichis anamountinsuicient to clog the pores. of the skin, anda lamination of cellular plastic bondedV with. the resin-of .the skin and. occupyingv theV pores ofl the. skinto beine- Y chanically secured thereto.

In an articleof ,manufacture.theccmbination of a porous fibrousV skinflaminatingY resin in the skin in the amount of from -to 30% by weight of the skin which is .anv amount insufficient-to clogthe pores of the. skinfandlalamination of cellular alkyd resin-polyisocyanateplastic bonded with the resin of the skin and occupying the. pores of the skin to be mechanically secured thereto.

6. In an article ofmanufacture the combination of a porous fibrousv skin, laminating resin in the skin inthe amount of` from15 to 30% by weight. of the skin Which is anamount insuficient to clogthe pores of the skin,and a lamination of cellular plastic, the plastic of the lamination being chemicallyunited'with said resin and occupyingsaid pores to be bonded both chemically and mechanically With said skin.

7. In an article of manufacture the combination of; a porousfabric skin, a non-volatile unsaturated resin deposited on, said skin in an amount insufficientV tok close the pores of' the skin, and a lamination of a cellular low-density alkyd resin-meta-toluene diisocyanate plastic, the plastic of the laminations being chemically united With said resinon the skin and entering the pores of the-skin.,`

8. An article of manufacture comprising spaced apart skins of porous fabric, resin on the fabric i. -of the skins, saidl resin leaving the pores of the vfabric open, and a lamination of cellular alkyd resin-diisocyanate-ethyl celluloseplastic cast between the skins to bondV with said resin and to occupy the pores in the fabric of the skin.

9. In an article of manufacture the combination of; `a skin` including a porous fabric, rst resin onthe fabric iny Van amount insuflicient to close the pores thereof and cured to render the skin substantially rigid, and a second resin on the fabric of the class adapted to copolymerize With isocyanate-containing molecules and a lamination of cellular alkyd resin-diisocyanate plastic cast against the skin so as to mechanically bond therewith and blend with said second resin to form an interfacial zonecontaining said second resin and said alkyd resin-diisocyanate.

10. An article of manufacture comprising spaced apart skins of porous fabric, cured resin on the fabric to render the same substantially rigid and in an insufficient amount to close the pores of the skin, a second resin on the fabric skins, and a core layer of cellular alkyd resindiisocyanate plastic copolymerized with said second resin and entering the pores -of the skins.

11. In an article of manufacture the combination of; a skin. including a porous fabric, rst resin on the fabric in an amount insufficient to close the poresv thereof and cured to render the skin substantially rigid, and a' second resin on the fabric of the class adapted to copolyinerize with isocyanate-containing molecules, and a lamination of cellular alkyd resin-diisocyanate plastic blended with said second resin and occupying the pores of the fabric tohave a chemical union and a mechanical lock with the skin.

12. An article of manufacture comprising a preformed skin including a porous fabric and a cured resin on the fabric in insufficient quantity to close the pores of the fabric, a layer of cellular alkydl resin-diisocyanate plastic, and an interfacial zone containing' molecules of said plastic and of a second resin and occupying the pores of the skin.

ELI SIMON. FRANK W. THOMAS. EDWARD I-I. BURKAR'I.

References ACited in the file of this patent UNITED STATES PATENTS Number Name Date 2,376,653V Boyerk May 22, 1945 2,377,846 Dreyfus et al June 5, 1945 2,414,125 Rheinfrank ,Jan. 14, 1947 OTHER REFERENCES Monsanto TechnicalV Bulletin No. P-145, March 16, 1950 (13 pages). 

1. AN ARTICLE OF MANUFACTURE COMPRISING SPACED SKIN LAMINATIONS OF FIBROUS MATERIALS, LAMINATING PLASTIC IMPREGNATED IN SAID MATERIALS, AND A CORE LAYER OF CELLULAR PLASTIC MATERIAL CAST BETWEEN SAID SKIN LAMINATIONS, THERE BEING INTERFACIAL ZONES AT THE PLANES OF JOINDER OF THE CORE LAYER AND SKIN LAMINATIONS CONTAINING SAID LAMINATING PLASTIC, SAID PLASTIC MATERIAL OF THE CORE LAYER, AND A COPOLYMER OF THE SAME. 